The present invention relates to radiation detectors and, more specifically, to a method and structure permitting the accurate alignment of an array of scintillator elements with individual domains of a pixelated photodiode array.
Radiation imaging detectors based on the combination of photodiode arrays and scintillator arrays are known. U.S. Pat. No. 5,773,829 to Iwanczyk and Patt, which is incorporated by reference in its entirety into the present disclosure, discloses such a radiation imaging detector. The components of such imaging detectors must be constructed and positioned to control the propagation of light from the scintillator array to the photodiode array. In one known form, the scintillator consists of numerous segments with optical reflectors between the scintillator segments. The optical reflectors reflect light back into the individual segments. Each segment of the scintillator array must be aligned with a respective photodiode pixel to detect light produced by the interaction of radiation with that scintillator segment.
Thus, there is a need to establish and maintain close alignment between the scintillator segments and the photodiode pixels so that light propagated from each individual segment of the scintillator array is detected by the photodiode associated with that segment and no others.
The present invention assures good reliability and precision in the assembly of critical components, namely scintillator arrays with photodetector arrays. By accurately aligning the scintillator array with the photodiode array and matching their physical cross-sections, the present invention provides a method for construction of imaging detectors which improves the signal-to-noise ratio for each radiation event, improves the spatial resolution, and reduces the crosstalk compared with conventional imaging detectors. These factors result in better quality of the displayed image.
In one embodiment, the invention involves the deposition and electrical coupling of a metallic grid pattern at the entrance window of the photodiode, thereby reducing the resistance of the transparent upper contact of the photodiode and providing a visually perceptible pattern by which a fabricator can accurately align the scintillator array with pixels of the photodiode. In addition, the scintillator array may be provided with open, light transmissive faces at opposite sides during fabrication, such that light can pass through the array in a direction parallel to the septa of the array. This permits the fabricator to align the scintillator array with the pixels of a photodiode placed adjacent one of the open surfaces, by visually monitoring the alignment through the second open surface. A suitable light reflective plate is then affixed to the second open surface of the scintillator array to cause light generated within the scintillator to be reflected internally until it reaches and is absorbed by the photodiode.
To realize the advantages outlined above, the structure and method of the present invention relate to a radiation imaging detector having a photodiode array formed from multiple pixels, a scintillator array formed from multiple segments and a grid on the surface of the photodiode array. The grid is disposed for ultimate positioning between the photodiode array and the scintillator array. Each of the segments is aligned with a cell of the grid which, in turn, is aligned with a pixel which is aligned with a contact on the opposite side of the photodiode array. The lines of the grid have a width equal to or somewhat greater than the thickness of the septa forming the walls of the scintillator segments. The individual scintillator segments have walls which are opaque to light, and the grid is geometrically matched to the segments and the pixels. The segments have open ends on opposing faces of the scintillator array and a light reflective plate is provided for affixing to one of the opposing faces after the scintillator array is aligned with the grid. The scintillator array is disposed to allow viewing of the grid through a first side prior to affixing the light reflective plate to the first side.
The radiation imaging detector can be fabricated by depositing a grid on the surface of a photodiode array so that the grid is aligned with multiple pixels forming the photodiode array; and aligning the scintillator array with the grid by viewing the grid through the first open end of the scintillator array so that the photodiode array, the scintillator array and the grid are aligned. The second open end of the scintillator array is coupled to the photodiode array and the first open end of the scintillator array is covered with a light reflective plate. The grid is deposited on the surface of the photodiode array in order to lower the series resistance of an entrance electrode of the photodiode array. The grid can be disposed above or below the entrance electrode of the photodiode array.